Microwave level gauge, or radar level gauges (RLGs), are in wide use for determining the filling level of a product contained in a tank. Radar level gauging is generally performed either by means of non-contact measurement, whereby electromagnetic signals are radiated towards the product contained in the tank, or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe acting as a guided wave transmission line.
In a GWR system, a probe is generally arranged to extend vertically from the top of the tank towards the bottom of the tank. Probes for GWR level gauge systems are typically provided in the form of wire probes or rigid probes. A wire probe may comprise a metallic wire having a diameter between a few mm up to tens of millimeters. Rigid probes often have a larger diameter.
In RLGs used in large tanks, such as tanks for liquid natural gas (LNG) which may be around 30 m high, wire probes are often used due to the ease of installation. Installation of a wire probe may comprise attaching a weight to the bottom of the probe and simply lowering the probe into the tank.
However, for certain applications it may be desirable, or even necessary, to use a rigid probe. A rigid probe is typically more robust and thereby more resistant against both mechanical wear and tear as well as chemical exposure. As is readily realized, a conventional rigid probe for use in large tanks formed in one piece can be difficult to both transport and install.
Furthermore, the varying size of tanks for different applications means that a level gauge system must be provided with a probe where the length is either tailor made for the specific tank, or where the length may be adjusted during installation.
To overcome the problems associated with using rigid probes in large tanks, U.S. Pat. No. 7,159,458 discloses a measuring device for determining the filling level of a product or the position of the interface between two media or phases in a container by means of high-frequency measuring signals which are guided along a waveguide. The waveguide comprises a wire cable with a plurality of individual wires of a predetermined diameter which are twisted together. U.S. Pat. No. 7,159,458 further discloses that the waveguide may comprise a plurality of pieces connected to each other via a flexible intermediate piece. The pieces may be tubes or rods, and the flexible piece may be a wire cable or universal joint.
However, the probe disclosed by U.S. Pat. No. 7,159,458 does not provide the possibility of reducing the amount of space required during transport of the probe and further may not provide a probe with the required rigidity for some applications.